Printing colored contact lenses

ABSTRACT

A method of making a colored contact lens comprises printing at least one layer of a colorant onto a contact lens using a printing process selected from the group consisting of ink jet printing, electrophotographic printing, thermal transfer printing, and photographic development printing. Printing can be done directly on the contact lens, on a film in a mold where the contact lens is formed, or on a cliché pad. Multiple layers of colorants can be printed onto a contact lens.

This application is a continuation of U.S. patent application Ser. No.09/879,013, filed Jun. 12, 2001, now U.S. Pat. No. 6,811,259, whichclaims under 35 U.S.C. § 119(e) the benefits of the filing dates of U.S.Provisional Patent Application Ser. No. 60/213,217 filed Jun. 20, 2000and of U.S. Provisional Patent Application Ser. No. 60/211,024 filedJun. 12, 2000, the contents of which are incorporated herein byreference.

BACKGROUND

For cosmetic purposes, contact lenses having one or more colorantsdispersed in the lens or printed on the lens are in high demand. Thesecolored contact lenses enhance the natural beauty of the eye, or provideunique patterns on the iris of the wearer.

Presently, methods of printing inks onto contact lenses involve clichéink transfer printing. A typical example of this printing follows. Animage is etched into metal to form a cliché. The cliché is placed on aprinter. Once on the printer, the cliché is inked by either an openinkwell doctoring system or by a closed ink cup sliding across theimage. Then, a silicone pad picks up the inked image from the cliché andtransfers the image to the contact lens. The silicone pads are made of amaterial comprising silicon that can vary in elasticity. The propertiesof the silicone material permit the inks to stick to the pad temporarilyand fully release from the pad when it contacts the contact lens.

There are several disadvantages associated with using cliché inktransfer printing to color contact lenses. This method lacksconsistency. Slight differences in the silicone pad can cause widevariation in image quality, effecting dot resolution and colorreproducibility. Further, multiple color layering is difficult and timeconsuming. Further still, the design and printing process using thismethod is slow. After an image is fully designed, it can take about twoweeks before that image is etched onto a cliché. The set-up ispainstakingly detailed and lengthy when more than one color is going tobe printed on the lens using this method. Presently, only three overlaysof color can be applied using this printing method. The difficulty andslowness of this printing method inhibits business strategies, making itdifficult to offer consumers a chance to design and print their owncontact lenses at the point of purchase.

A printing apparatus and printing method are needed that can producehigh quality images in a consistent manner on contact lenses. A simple,quick, and highly precise printing apparatus and method are needed whenmultiple colors are being printed onto a contact lens, preferably onethat permits consumers to design and print their own contact lenses whenthey purchase those lenses.

SUMMARY OF THE INVENTION

The products and processes of the present invention address at leastsome of the difficulties in the prior art.

In one aspect of the invention, a method of making a colored contactlens comprises printing at least one layer of a colorant onto a contactlens using a printing process selected from the group consisting of inkjet printing, electrophotographic printing, thermal transfer printing,and photographic development printing.

In another aspect of the invention, a method of making a colored contactlens comprises: (a) printing a first layer of a colorant in a firstpattern onto a contact lens using a printing process selected from thegroup consisting of ink jet printing, electrophotographic printing,thermal transfer printing, and photographic development printing; (b)printing at least one second layer of a colorant in a second patternonto a contact lens using a printing process selected from the groupconsisting of ink jet printing, electrophotographic printing, thermaltransfer printing, and photographic development printing; and (c)coating the colored contact lens with a binding solution comprising amonomer or a polymer.

In still another aspect of the invention, an improved method of makingcolored contact lenses comprises printing at least one layer of acolorant onto a contact lens using a printing process selected from thegroup consisting of ink jet printing, electrophotographic printing,thermal transfer printing, and photographic development printing.

The present invention provides the foregoing and other features, and theadvantages of the invention will become further apparent from thefollowing detailed description of the presently preferred embodiments,read in conjunction with the accompanying figures. The detaileddescription and figures are merely illustrative of the invention and donot limit the scope of the invention, which is defined by the appendedclaims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows electrophotographic printing onto contact lenses using aphotosensitive sphere.

FIG. 2 shows electrophotographic printing onto contact lenses using aphotosensitive hemisphere.

FIG. 3 shows thermal transfer printing onto contact lenses.

FIG. 4 shows a top view of the thermal transfer printing of FIG. 3.

FIG. 5 shows a cross section of the lens in FIG. 3 after it has beenprinted on using thermal transfer printing.

FIG. 6 shows photographic transfer printing onto contact lenses.

FIG. 7 shows an image printed onto a contact lens by photographictransfer printing.

DETAILED DESCRIPTION Definitions

“Colorant” means either a dye or a pigment or a mixture thereof.

“Dye” means a substance that is soluble in a solvent and that is used toimpart color. Dyes are typically translucent and absorb but do notscatter light. Dyes can cover both optical regions of contact lenses andnon-optical regions of contact lenses.

“Fluorescence” means luminescence caused by absorption of visible lightor ultraviolet radiation at one wavelength followed by nearly immediateemission at a longer wavelength. Fluorescent emission ceases almostimmediately when the light or incident ultraviolet radiation stops.

“Monomer” means low molecular weight compounds that can be polymerized.Low molecular weight typically means average molecular weights less than700 Daltons. The term “monomer” also refers to medium and high molecularweight compounds or polymers, sometimes referred to as macromonomers,(that is, typically having number average molecular weights greater than700) containing functional groups capable of further polymerization.

“Pearlescence” means having a pearly luster; resembling a pearl inphysical appearance; or having a nearly neutral slightly bluish mediumgray color.

“Phosphorescence” is luminescence caused by the absorption of radiationat one wavelength followed by delayed emission at a differentwavelength. Phosphorescent emission continues for a prolonged time afterthe incident radiation stops.

“Pigment” means a powdered substance that is suspended in a liquid inwhich it is relatively insoluble. Pigments are used to impart color.Because pigments are in the form of a suspension, they tend to have anopacity quality. That is, they reflect light and obstruct the passage oflight. For this reason, it is preferred that pigments are located innon-optical regions of a contact lens.

“Polymer” means a material formed by polymerizing one or more monomers.

The Contact Lenses

The methods of the present invention involve printing a colorant onto acontact lens using ink jet printing, electrophotographic printing,thermal transfer, or photographic development. The image is preferably adigital image, but it can also be an analog image.

In one embodiment, the contact lenses are transparent before they areprinted upon. In another embodiment, the contact lenses are tinted priorto being printed upon. That is, a colorant may have been dispersed inthat lens using methods that are well known in the art before that lensis printed upon using digital technology.

In another embodiment, the contact lenses that are going to be printedupon can optionally have been pre-printed using methods that are wellknown in the art. The well known methods include the ones disclosed inU.S. Pat. No. 5,116,112, which is hereby incorporated by reference. Thismethod involves coating a colored liquid (which is either thermosettingor thermoplastic) in a mold for making a contact lens onto a surfacethereof where the iris portion of the lens is formed to produce acolored film providing a pattern thereon which film contains a surfaceexposed to the interior of the mold and a surface in contact with themold; and charging the mold with the lens-forming liquid used to formthe body of the lens while maintaining the colored film in the irisportion and configuring the lens-forming liquid about the colored filmwhereby the surface of the film becomes integral with the body of thelens and surface of the film becomes part of the outer surface of thelens when the molded lens is removed from the mold.

Ink Jet Printing

Preferably, the colorant applied to the contact lens using an ink jetprinter is an ink. A preferred ink contains at least one dye. Nearly anydye can be used in the present invention, so long as it can be used inan ink jet printer. These dyes include fluorescent dyes, phosphorescentdyes, pearlescent dyes, and conventional dyes.

A preferred ink contains at least one pigment. Nearly any pigment can beused in the present invention, so long as it can be used in an ink jetprinter. Preferred pigments include fluorescent pigments, phosphorescentpigments, pearlescent pigments, and conventional pigments. Pigments caninclude any colorant permitted in medical devices and approved by theFDA, such as D&C Blue No. 6, D&C Green No. 6, D&C Red No. 17, D&C VioletNo. 2, D&C Yellow No. 10, carbazole violet, certain copper complexes,certain chromium oxides, various iron oxides, phthalocyanine green,titanium dioxides, etc. See Marmiom D M Handbook of U.S. Colorants for alist of colorants that may be used with the present invention.

The pigment should be much smaller than the orifice in an ink jet nozzleto prevent clogging during the printer process. Generally, this meansthat preferred pigments are 3 microns or smaller. Larger pigments can beground into smaller particles to reduce potential clogging. Preferredmethods of reducing a pigment's particle size include high speed mixers,Kady Mills, colloid mills, homogenizers, microfluidizers, sonalators,ultrasonic mills, ball mills, roller mills, vibrating ball mills,attritors, sand mills, varikinetic dispensers, three-roll mills, Banburymixers, or other methods well known to those of skill in the art.

The preferred ink has a surface tension of at least 35 mN/m. Any surfacetension parameter is acceptable so long as the ink jets adequatelyspreads when it contacts the lens. Preferably, the ink breaks intowell-defined streams of droplets based upon its surface tension. Thesurface tension of the ink can be adjusted by adding or removingdiluents or surfactants.

It is preferred, but not necessary, that the ink dry in less than 5seconds. It is preferred that the ink adhere to the lens and that thelens retain its shape after being treated in an autoclave.

A preferred ink has organic solvents. Preferred solvents require somepolarity to dissolve a binder. Preferred solvents have few functionalgroups that compete with the isocyanate cross-linking system such asalcohol groups, amine groups, and acid groups. A preferred ink cancontain many solvents, including glycols, ketones or esters.Cyclopentanone is a particularly preferred solvent. A preferred inkcould optionally contain humectants (e.g., ethylene glycol) andsurfactants.

It is also preferred, for continuous ink jet operation, that the ink ischarged by an electrode to drop away from the gutter and onto theprinting surface. This can be achieved by many ways well known in theart, including by adding about 0.5% by weight of a salt.

The preferred ink flows easily in ink jet applications. Preferably, theink has a viscosity of from about 1 centipoise to about 50 centipoise.More preferably, the viscosity is from about 2 to about 30 centipoise.Most preferably, the viscosity is between 5 and 15 centipoise.

The colorants can be printed in a single layer or in many layers, and inany pattern that achieves desirable cosmetic effects. Preferred patternsof colorants include those identified in U.S. Pat. Nos. 5,936,705;5,414,477; and 5,272,010, which are hereby incorporated by reference.

The patterns that the single or multiple layers of colorants form on thecontact lenses are preferably comprised of zones, and the zones may becomprised of shaped colored regions within the zones. The shaped regionmay further be comprised of dots. Examples of zones include: a singleannular iris color zone with irregular inner and outer borders, multipleconcentric annular zones, annular zones with outer and inner starbursts,and a single iris zone but irregular in structure along multiple radiallines. Examples of shaped colored areas within zones include circularareas, ovular regions, irregular elongated regions in worm-like shapes,radial segments, and combinations of these shapes

The addition of surfactants, particularly ionic surfactants, may behelpful for optimal color dispersion.

In a preferred embodiment, the colored contact lens is coated with abinding solution. Binding can occur during or after printing. It ispreferred that the binding solution be applied to only those regions ofthe contact lens that are not in the optical zone, or the zone of thecontact lens through which one sees.

The process of coating the contact lens can be done by any method thatis well known in the art. In one embodiment, the binding solution couldbe sprayed onto the lens. If this method is used, a mask should beplaced over the optical zone of the lens before spraying occurs. Inanother embodiment, the binding solution could be coated onto the lensusing printing pads.

The preferred solvent of the binding solution depends upon the method ofcoating used. If the spraying method of coating is used, the solventshould have a low viscosity. That is, it is preferred that the viscositybe less than 50 centipoise. If the printing pad method of coating isused, the solvent should have a higher viscosity. That is, it ispreferred that the viscosity be greater than 100 centipoise. Viscositycan be adjusted by the addition or subtraction of polymer chains or bythe addition or subtraction of a solvent. Organic mixtures are thepreferred solvents.

Preferably the binding solution comprises at least one monomer. Morepreferably, the binding solution comprises at least one hydrophilicmonomer and at least one hydrophobic monomer. Nearly any hydrophilicmonomer that can act as a plasticizer can be used. The hydrophilicmonomer can allow the printed material to deform with the lens withoutcracking. Among the preferred hydrophilic monomers are 2-hydroxyethylmethacrylate (HEMA), n-vinylpyrolidone (NVP), glycerylmethacrylate(GMA), and N,N-dimethyacrylamide (DMA). This list is exemplary, notlimiting.

Nearly any hydrophobic monomer can be used to improve the strength ofthe coating and to improve the solubility of the monomer in organicsolvents. Among the preferred hydrophobic monomers are 2-ethoxyethylmethacrylate (EOEMA), methyl methacrylate (MMA), and n-butylmethacrylate (BMA). This list is exemplary, not limiting.

Preferably, the binding solution contains an initiator. Preferably, a UVor heat-activiting initiator is used.

Preferably, the binding solution makes a tightly cross-linked film thattraps the colorants in the film. For this, it is preferable to addethylene glycol dimethacrylate. Hexamethylenediisocyanate (HMDI) isanother preferred crosslinker. This list is exemplary, not limiting.Swelling agents are preferably used to allow penetration of the monomerinto the contact lens and they improve adhesion. Preferred swellingagents include cyclopentanone, cyclohexanone, or methyl ethyl ketone.This list is exemplary, not limiting.

Preferably, the binding solution contains an adhesion promoter.Preferably, the adhesion promoter is HMDI. Nearly any adhesion promotercan be used, including those disclosed in U.S. Pat. No. 5,272,010, whichis incorporated by reference herein.

Preferably, the binding solution contains a chain transfer agent.Preferably, the chain transfer agent is mercaptoethanol.

Any ink jet printer can be used with the present invention so long as itcan be configured to print the inks as described above on contact lensesthat have curved surfaces. The TRIDENT OPTIJET 2 printhead is apreferred printhead available from the Trident Corp. in Park Ridge, Ill.

A preferred ink jet printer is either drop-on-demand (DOD) orcontinuous-jet. Many continuous ink jet printers could be used, fromcompanies such as Domino-Amjet, Videojet, Scitex Digital Printing,Willet, Linx, Iris Graphics, Stork, and Dupont. Many DOD printers couldbe used, from companies such as Epson, Xaar, Hitachi, Spectra,Tektronix, Canon, Hewlett-Packard, Lexmark, Olivetti, Xerox, Panasonic,VUTEk, and NEC.

A preferred ink jet printer can print pixels of less than 150 microns indiameter, preferably less than 100 microns in diameter. Pixel size ismeasured using standard microscopy techniques, which are well known tothose of skill in the art. A preferred ink jet printer can space thepixels less than 80 microns from each other, preferably less than 50microns from each other. To, achieve this result, it is preferred thatthe drops of ink that are emitted from the nozzle have a volume of lessthan 100 picoliters, preferably less than 50 picoliters, and morepreferably, less than 10 picoliters.

A preferred ink jet nozzle is sized to form drops of the preferredvolume given the ink viscosity and thermal forces. Preferably, thenozzles can face perpendicular to the lens surfaces, forming ahemisphere around the lens. Alternatively, the lens surface could berotated. It might also be usful to index the printer head with the lensrotator for non-radially symmetrical lenses with a non-symmetricalpattern.

In a preferred embodiment, the ink jet heads are controlled through theuse of a computer.

In a preferred embodiment, batch processing could be used to print manycontact lenses in rapid succession. For example, a batch of eight lenses(one palate) could be sent to eight printer heads. Lifts push the lenscup to put it in the vicinity of the printer heads. The cups could berotated in a controlled fashion. The print heads would jet on and offbased upon instructions sent from the computer software. The lifts wouldthen lower the lenses back on their palate. Then, the palate would besent through a system to print or spray the binding solution over thelenses. Then, the lenses would be sent to a curing process to heat anddry the lenses.

Through routine experimentation, one of ordinary skill in the art canoptimize the process of printing colorants onto contact lenses usingvarious quantifiable analytical techniques.

Electrophotographic Printing

Electrophotographic printing includes laser printing. Referring to FIG.1, a preferred embodiment is shown. A toner drum 8 transmits toner tocontact lens 6 via a photosensitive metal sphere 9. In this embodiment,metal sphere 9 rolls over contact lens 6.

Referring to FIG. 2, a toner drum 18 transmits toner to a photosensitivemetal hemisphere 19. In this embodiment, lens 16 is placed over thehemisphere 19 after the toner has been printed on the hemisphere 19. Thelens 16 is printed on an internal surface.

Generally, electrophotographic printing works as follows. Acomputer-controlled light source (laser 4 in FIG. 1, laser 14 in FIG. 2)in electrical communication with an RGB (red, green, blue) signal(signal 2 in FIG. 1, signal 12 in FIG. 2) is directed to aphotosensitive drum (drum 8 in FIG. 1, drum 18 in FIG. 2), whichattracts charged toner particles where exposed.

Print quality is adjusted by varying the charge to attract differentconcentrations of toner. The toner is then transferred by rolling thecontact lens across the drum using rollers.

For contact lenses, the photosensitive metal sphere 9 or hemisphere 19could be used instead of the more traditional photosensitive drum. Lightwould be used to charge the sphere 9 or hemisphere 19. Toner particles,one color at a time, would then be exposed to the sphere 9 or hemisphere19. The sphere 9 or hemisphere 19 could then contact a surface of acontact lens 6 or contact lens 16 to transfer the toner to a surface,either external or internal, of the contact lens 6 or 16.

Alternatively, the lens could contain a photoconductive monomer such asvinyl carbazol. This would allow the lens to be placed directly on thephotosensitive hemisphere 19. Light would charge the lens surfacedirectly to allow toner particle transfer without the need for anadditional toner transfer process.

Compressional forces (via rollers, balls, molds, etc.) could be used tofacilitate toner transfer. Adhesive agents such as those that are wellknown in the art could be added before or after printing to ensurecolorfastness.

Thermal Transfer Printing

Referring to FIGS. 3–5, one embodiment of thermal transfer is shown. AnRGB signal 22 is in communication with thermal head 24. Thermal head 24allows heat to pass through a donor ribbon 27, allowing the color ofdonor ribbon 27 to pass onto contact lens 26. In the depictedembodiment, donor ribbon 27 has three sections wherein the first sectionis yellow, the second section is magenta, and the third section is cyanso that only one color is transferred to the contact lens 26 at a time.In another embodiment, there could be one ribbon for each color that isto be printed. Donor ribbon 27 is supported on spools or rollers 23 and25.

FIG. 4 is a top view of FIG. 3 taken along line 44. FIG. 5 is a crosssection of contact lens 26 taken along line 5—5 after it has beenprinted upon using thermal transfer. Layer 26 is the contact lens, layer31 is yellow, layer 32 is magenta, and layer 33 is cyan. In analternative embodiment, the order in which the color layers are printedonto the contact lens is alternated.

Thermal transfer technology relies upon the transfer of image-formingdyes or colored waxes onto a substrate such as a contact lens 26 or afilm for use in a mold where a contact lens is formed. An analog imageor a digital computer image desired is broken into its RGB constituentsusing standard color separation techniques.

A three-color complement system such as CMY (cyan, magenta, and yellow)can be used as the colorant media to absorb the corresponding color(cyan absorbs red, etc.). Each color layer is broken down into a rastersignal, which controls a thermal head 24 that sequentially passes over acyan, magenta, and yellow dye or wax donor ribbon 27. Applying heatcauses the donor ribbon 27 to transfer its colorant onto the substrate(either contact lens 26 or a film for use in a mold where a contact lensis formed) passing underneath the ribbon 27. After passing over allthree sections of ribbon 27, a three-layered surface is formed on thesubstrate (contact lens) composed of the different colors, as shown inFIG. 5. Process color could be used to form secondary and tertiarycolors.

The ribbon 27 may be flat (typical of printing onto flat substrates) androlled across the surface of the lens using rollers. A preferred methodwould use a curved hemispherical-shaped ribbon to facilitate printing onthe hemispherical contact lenses.

Printing Using Photographic Developing

Referring to FIGS. 6 and 7, a digital displayed image 40 is reproducedas an image 44 printed onto contact lens 36. Light burns the image 40onto film 35. Film 35 has three light-sensitive layers. Layer 37 is bluesensitive, layer 38 is green sensitive, and layer 39 is red sensitive.The contact lens is then chemically treated using film developingprocesses well known in the art. Layer 37, which is blue sensitive,forms as much of its complementary color (yellow) as layer 37 a as isnecessary to reproduce image 40. Likewise, layer 38, when processed,forms its complementary color as layer 38 a, and layer 39 forms itscomplementary color as layer 39 a. Excess material not necessary forreproduction of the image 40 is either washed away during chemicaltreatment or is clear after chemical treatment.

Photosensitive dyes may be used for digital image capturing, similar tothe well-known technology used for photographic transparencies. A filmcomposed of three light-sensitive layers (corresponding to blue, green,and red) is deposited on the contact lens surface or the surface of afilm for use in a mold where a contact lens is formed.

A computer-controlled light source (such as a cathode-ray tube) is usedto expose the color-sensitive layers. The film is then chemicallyprocessed to form the complementary colors to be presented on thesurface being printed upon. The chemical processing or film developmentis done using technology that is well known in the art.

Exemplary Uses of Digital Printing

Digital printing methods and systems of the present invention can finduse in printing on contact lenses cosmetic patterns including iris-likepatterns, WILD EYE™ patterns, made-to-order (MTO) patterns, and thelike. Design changes in cosmetic patterns can be implemented easily,especially across different lens materials and products. The patternprinted by digital printing methods and systems of the present inventioncan have improved resolution and may be richer in detail. Digitalprinting methods and systems of the present invention also allowcustomers to design any images or patterns to be printed.

Digital printing methods and systems of the present invention can alsofind use in printing on contact lenses inversion marks. Currently, aninversion mark that allows a user to handle and insert easily a contactlens, for example, a FRESHLOOK™ contact lens (Wesley JessenCorporation). The printed inversion mark is easier to identify and usethan other inversion marks made by non-printing methods includingetching, positively molding, or laser etching. The printed inversionmarks could also provide stronger lenses, since no material is removedand removal of materials from lenses could cause stress propagationsites. In addition, the printed inversion mark may have less adverseimpact on wear comfort, especially with a print-on-mold system.Potentially all contact lens can be printed with an inversion mark. Thedigital printing methods and systems of the present invention can printinversion marks rapidly, potentially faster than pad printing.

Digital printing methods and systems of the present invention can alsofind use in printing on contact lenses stock keeping units (SKUs).Material handling and packaging is always an issue with a large numberof SKUs. The digital printing system may allow SKU codes, either informs of numbers or as bar codes, to be printed either on a mold or insmall print on a contact lens itself. In a preferred embodiment, smallprints of SKU codes is blended in with an iris pattern or any othercosmetic pattern or inversion marks. In another preferred embodiment,SKU codes is printed discretely in black to be hidden by the iris or inwhite to be hidden by the sclera. In a further preferred embodiment, aniris pattern is coded to represent SKUs, for example, two thickstriations followed by two thin striations represents lenses having aprescription of −3.00 D. By printing SKU codes on contact lenses, thedigital printing systems of the invention can aid in monitoring productflow and in verifying product identity in the manufacturing contactlenses. There would be fewer labeling mistakes since every lens could beidentified quickly.

Digital printing methods and systems of the present invention canfurther find use in printing identity verification marks on contactlenses. By printing an identity code, such as a bar code, number code,special iris pattern, or any other coding system, onto a contact lens,the identity of a contact lens wearer can be verified by reading theidentity code with a simple camera system, preferably the camera systemhaving colored filters. Preferably, the identity codes are printed oncontact lenses with fluorescent or phosphorescent inks. Such a systemcan be used for access to buildings, secure rooms, home security system,ATMs, internet sites, and the like. A potential advantage of using thissystem is that only a person with the correct eye prescription can usethe ID coded contact lens.

Scope

It can be seen that the present invention provides colored contactlenses capable of changing the appearance of the wearer's iris and ofproviding cosmetic effects, inversion marks, SKU codes, and identitycodes. Various changes may be made in the function and arrangement ofparts: equivalent means may be substituted for those illustrated anddescribed; and certain features may be used independently from otherswithout departing from the spirit and scope of the invention as definedin the following claims.

1. An ink for printing a pattern on a curved surface of a contact lens,comprising at least one pigment having a size of 3 microns or smaller,wherein the ink is characterized by having a viscosity of from about 1to about 50 centipoise and being capable of adhering to the contact lensafter being treated in an autoclave.
 2. The ink of claim 1, wherein theink is further characterized by being capable of drying in less than 5seconds.
 3. The ink of claim 1, wherein the ink has a surface tensionsufficient to allow the ink to adequately spread when the ink contacts asurface of the contact lens.
 4. The ink of claim 3, wherein the surfacetension of the ink allows the ink to be broken into well-defined streamsof droplets.
 5. The ink of claim 4, wherein the ink has a surfacetension of at least 35 mN/m.
 6. The ink of claim 3, wherein the ink isfurther characterized by being capable of drying in less than 5 seconds.7. The ink of claim 4, wherein the ink is further characterized by beingcapable of drying in less than 5 seconds.
 8. The ink of claim 6, whereinthe viscosity of the ink is from about 5 to about 30 centipoise.